There's a film called Zeitgeist which has become very popular online. It is divided into several different sections - one is about religion, there are others about the banking system and 9/11. The section about religion is here, for reference (it's the first section in the film).

It compares Jesus with other historical deities - Mithra, Mithras, Horus, etc and essentially it tries to portray Christianity as a "copycat" religion. For example, it says that all of these deities - Jesus included - were born of a virgin on December 25th. But these claims, which are portrayed as facts - don't have any factual basis or evidence to support them as far as I can determine. It honestly seems like the authors of Zeitgeist outright made them up to promote atheism.

There's a more worrying part elsewhere in the film about JFK which I've written about before. For that part, I find it difficult to see how it can be anything other than a deliberate attempt at deception by the authors of the film. With that in mind, I think it's wise to be very cautious about any of the claims made by that film, the religion section included.

EDIT: For reference, here are the main deities that Zeitgeist lists, along with Wikipedia links to pages about them. Tell me if these sound similar to the Christian story:

Attis: "Pausanias was told that the daemon Agdistis initially bore both male and female attributes. But the Olympian gods, fearing Agdistis, cut off the male organ and cast it away. There grew up from it an almond-tree, and when its fruit was ripe, Nana who was a daughter of the river-god Sangarius picked an almond and laid it in her bosom. The almond disappeared, and she became pregnant. Nana abandoned the baby (Attis). The infant was tended by a he-goat. "

Krishna: "Krishna belonged to the Vrishni clan of Yadavas from Mathura, and was the eighth son born to the princess Devaki, and her husband Vasudeva."

Dionysus: "His mother was a mortal woman, Semele, the daughter of king Cadmus of Thebes, and his father was Zeus, the king of the gods. Zeus' wife, Hera, discovered the affair while Semele was pregnant."

Mithra: (Wikipedia doesn't say anything about his birth)